1. Field of the Invention
The present invention pertains broadly to the shaping of heated glass sheets, and more particularly to the shaping of such glass sheets while being conveyed upon a series of specially configured, pivotable conveyor rolls beneath correspondingly configured reciprocable top rolls.
2. Description of the Prior Art
In mass producing curved or bent glass sheets employed as glazing closures for automobiles and the like, glass sheets are commonly advanced along a horizontal path on roll-type conveyors successively through a heating area, a bending area and a heat treating area for annealing or tempering the bent or shaped sheets. As the sheets advance through the heating area they are gradually heated to approximately the softening temperature of the glass, and then quickly advanced into the bending area for shaping to the desired configuration. Following bending, the shaped sheets which are to be tempered are quickly advanced into a tempering area between opposed blastheads and subjected to opposed high-velocity streams of cooling air directed against their opposite major surfaces.
In accordance with one widely used process for producing such shaped sheets, the heated sheets are advanced from the heating furnace into the bending area and accurately located therein between complemental upper and lower shaping members by locating stops positioned in the path of an advancing sheet for engaging the leading edge thereof. The sheet is then engaged around its peripheral marginal edge portion by a lower press member and lifted from the conveyor rolls into engagement with an upper complemental press member for press bending to the desired configuration. Upon completion of bending the lower press member is retracted to deposit the bent or shaped sheet upon the conveyor rolls for advancement into and through the tempering area.
As the sheet is advanced into the bending area its movement is stopped by engagement with the locating stops. The conveyor rolls continue to rotate, and even if lifting of the sheet begins simultaneously with interruption of the advancement, the heated central portion of the sheet inwardly from the press member-contacting peripheral margins will sag somewhat to remain in contact with the rotating conveyor rolls for a brief period. The resulting frictional contact can mar the surface of the hot glass and cause an objectionable optical defect known as "roll distortion". In order to alleviate this problem a system was devised, as disclosed in U.S. Pat. No. 3,905,794, wherein a series of rolls having arcuately curved central portions is provided within the bending apparatus. The rolls are pivotable in unison between a first position whereat the central portions lie in a common horizontal plane for conveying the flat sheet, and a second position whereat the central portions are out of engagement with the sheet and at an angle to the horizontal plane. An improvement to the actuator mechanism for adjusting the angular attitudes of the rolls is described in U.S. Pat. No. 4,015,968. While the devices somewhat alleviated the above-noted problem of roll distortion, they still required interruption of the advancement of each sheet and subsequent acceleration of the bent sheet from a static position. The stopping, lifting, lowering and accelerating not only create opportunities for formation of optical defects such as roll distortion, but the procedure is also time consuming so as to result in an extended cycle time for the bending of each sheet.
It has also been proposed to shape glass sheets by a so-called roll forming process wherein the heated sheets are passed between opposed rolls having complementary configurations defining a pass therebetween which bends the sheets to the desired shape. Such devices are disclosed, for example, in U.S. Pat. Nos. 3,545,951, 3,701,644, 4,381,933 and 4,556,406. However, none of the devices has proven entirely satisfactory in shaping glass sheets at the rates and with the optical quality necessary for modern day production lines.